Pebble heater apparatus and method of regenerating pebbles therein



L J`. WEBER PEEELE HEATER APPARATUS AND METHOD 0E REGENERATING PEBELEs THERETN nu: @as Alva nur MAN/Paw FUEL 645 CONDU/T March 3, 1953 Elled Dec :51, 194s March 3,1953 L. J. WEBER 2,630,413

PEBBLE HEATER APPARATUS AND METHOD 0F REGENERATING PEBBLES THEREIN' Filed Dec. 31, 1948 3 Sheets-Sheet 2 FIG. 2

INVENTOR.

L. J. WEBER A T TORNEI/5 March 3, 1953 J. WEBER 2,630,413

v PEBBLE HEATER APPARATUS AND METHOD oF REGENERATTNG PEBBLES THERETN INVENTOR.

L J. WEBER A TTORNE Y Patented Mar. 3, 1,953

PEBBLE HEATER APPARATUS AND METHOD OF REGENERATING PEBBLES THEREIN Louis J. Weber, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application December 31, 1948, Serial No. 68,467

13 Claims. 1

This invention relates to pebble heater apparatus. In one of its more specific aspects it relates to thermal conversion apparatus. In another of its more specirlc aspects it relates to pebble heating chambers of pebble heater apparatus. In still another of its more specific aspects it relates to pebble regeneration chambers of pebble heater apparatus.

Thermal conversion or treating processes car-- ried on in so-called pebble heater apparatus utilize a flowing mass of pebbles which is heated to a high temperature by passing hot gases therethrough, in a first direct heat exchange step,

and is then caused to contact a reactant fluid,

urnishing heat thereto, in a second direct heat exchange. The conventional pebble heater ap paratus comprises two chambers which may be disposed in substantially vertical alignment. A solid heat exchange material, such as refractory pebbles, is introduced into the upper portion of the rst chamber. The solid heat exchange material flows downwardly through the chamber in direct heat exchange with a hot gaseous heat exchange material. The solid heat exchange material is heated to a high temperature in the heat exchange and is then passed to a second chamber in which the hot solid heat exchange material is caused to contact a fluid in a second direct heat exchange relation, furnishing heat for the treatment or conversion of the luid.

Many conventional pebble heaters are provided with a combustion chamber adjacent or in close proximity to the lower portion of the rst chamber. A hot combustion gas from the combustion chamber is injected through the sides or into the bottom of the rst chamber, better known as the pebble heating chamber. Pebbles which pass downwardly through the heating chamber contact the rising combustion gas and are heated as above described. One disadvantage cf such conventional pebble heater apparatus is that pebbles near the periphery of the pebble bed in the heating chamber are heated to a higher temperature than those in the centei` of the downwardly flowing bed. This is due to the fact that a greater portion of the combustion gas tends to take the path of least resistance through the pebble bed. In most conventional pebble apparatus, pebbles are introduced into the pebble heater chamber through a single opening in its top. Pebbles are withdrawn from a point substantially centrally located in the bottom area of the heating chamber. As pebbles flow through thechamber, they tend to form acone downwardly and outwardly from the pebble inlet, and the pebbles flowing out of the chamber tend to form an inverted cone downwardly and inwardly toward the pebble outlet. It will be seen that due to the cone shaped top and bottom of the bed, the area near the periphery is usually the thinnest and the point of least resistance for upwardly flowing gas. Gas tends to pass directly upwardly from the gas inlet, through the periphery of the bed and out of the eiuent (flue-gas) outlet in the top of the chamber. A portion of the pebble bed below the moving cone of pebbles is relatively stagnant. Once these pebbles in the stagnant area are heated they lose very little of their heat and thus receive very little heat from the .gas passing upwardly therethrough. For that reason, gas leaving the heating chamber through the effluent outlet carries with it a considerable amount of heat which could have been imparted to cooler pebbles flowing downwardly in the central portion of the chamber.

In conventional pebble heating chambers the pebbles are heated by means of a hot ilue-gas generated in a chamber separate and external to the chamber containing the pebbles. Construction for such an arrangement is expensive and dilcult. Since the usual pebble bed contains approximately 50 per cent void space, heretofore. the smallest flue-gas passage was through a ceramic dome or other screen between the fluegas chamber and the pebble heating chamber containing the pebbles. Also, in conventional pebble heating chambers the ratio of height to diameter is maintained usually less than 1:1 because the combustion gases :flow countercurrent to the flow of pebbles and a high bed depth creates too great a pressure drop. In the novel pebble heating chamber and method of my invention the restriction between the nue-gas chamber and the pebble bed has been removed and flue-gas pressure drop has been reduced. In addition, construction and maintenance is simplified. In the novel apparatus and method or" my invention combustible material passes into the pebble bed normal to the path of flow of the pebbles and the combustible material is burned on the surface of the pebbles. Combustion products are withdrawn from points opposite the combustible mixture inlets. Since the ilow of heating gases is normal to the path of flow of the pebbles a relatively large height to diameter ratio of the pebble bed may be used thus appreciably minimizing the problems in conventional vpebble heating chambers of stagnant pebbles with low height to diameter ratios and high pressure drop with high height to diameter ratios. Heat input may be regulated to any zone within the pebble heating chamber by proper regulation of fuel-gas and oxygen-containing gas to burners or mixers which are spaced at a plurality of elevations along the height of the pebble bed.

Furthermore, with a typical pebble heating chamber with a separate combustion zone, it is necessary to compress a considerable amount of air or oxygen-containing gas in excess of that required for combustion in order to have a suiiicient rvolume of flue-gas to carry the heat released in the combustion zone to the pebble bed. This procedure is necessary to avoid burning up the combustion zone which has no heat absorbing surfaces. Thi-s means that the quantity of fluegases passing from the bed and out of the chamber is greater than desired; and since these gases are at a relatively high temperature, the thermal efficiency of the unit is greatly reduced. In the novel apparatus and method of my invention this difficulty is overcome, because a combustible mixture of fuel-gas and an oxygen-containing gas at approximately stoichiometric concentrations is passed into the pebble bed and combustion is carried out on a heat absorbing surface, namely the pebbles. In addition, the flue-gases exiting from the pebble heating chamber are recycled to the wind-box or manifold of my apparatus. The flue-gases before entering the Wind-box or manifold are tempered and blended with air or an oxygen-containing gas in suincient quantity to provide oXygen for the burning of entering fuel-gas. Thus the quantity of air or other oxygen-containing gas which must be compressed is substantially reduced and by recycling the flue-gases the amount of heat lost from the unit in eiuent flue-gas is likewise reduced. Only the amount of air or oxygen-containing gas necessary to provide oxygen for combustion is heated when the heating chamber is in operation. Also, one of the valuable advantages ofthe apparatus and method of my invention is the provision for the injection of the desired amount of heatat any level of the pebble heating chamber. Since the amount of heat injectionv into any level of the pebble bed may be controlled, it is possible to raise the pebbles to the iinal high temperature level desired just before they pass from the pebble heating chamber. This is an` advantage since the pebbles are exposed to the desired high temprature for only a very short period of time, and refractory pebbles which have a tendency to sinter or spall may be used much more satisfactorily than with a typical chamber wherein a substantial volume of the pebbles are subjected to a high temperature for extended periods of time. For this reason it is possible to heat pebbles by the method and apparatus of my invention to a higher temperature than is possible with the usual type of pebble heater method and apparatus.

An object of my invention is to provide an improved chamber for heating pebbles in pebble heater apparatus.

Another object is to provide an improved method for heating pebbles in pebble heater apparatus.

Another object is to provide anl improved means for transporting a pebble bed within the heating chamber of pebble heater apparatus.

Still another object of my invention is to providemeans andwmethod for more evenly heating 4 a flowing pebble bed in a heating chamber of pebble heater apparatus.

Still another object of my invention is to provide apparatus and method for regenerating and heating pebbles in a pebble regeneration and/or heating chamber of pebble heater apparatus.

Other and further objects will be apparent, to those skilled in the art, on reference to the accompanying discussion, drawings and claims.

The term pebble as used herein denotes any solid refractory material of owable form, size and strength which is suitable to carry a large amount of heat from the pebble heating chamber to the fluid heating chamber. Pebbles conventionally used in pebble heater apparatus are substantially spherical in shape and are from about 1/8 inch to about 1 inch in diameter. In a high temperature process, pebbles having a diameter of between about 1/4 inch to about inch are preferred. The pebbles must be formed of a refractory material which will withstand temperatures at least as high as the highest temperature attained in the pebble heating chamber. The pebbles must also be capable of withstanding temperatcre changes within the apparatus. Refractory materials, such as a metal alloy, ceramic, or other satisfactory material, may be utilized to form such pebbles. Satisfactory pebbles may be formed of silicon carbide, alumina, periclase, beryllia, stellite, zirconia and mullite in admixture with each other or with other materials. Pebbles formed of such materials, when properly fired, serve very well at high temperatures, some withstanding temperatures up to about 3500 F. Pebbles which are inert or catalytic may be used in selected processes.

Understanding of my invention will be facilitated upon reference to the attached diagrammatic drawings in which Figure 1 is a vertical section of a preferred pebble heating chamber embodying my invention, particularly well suited to carry out even heating of pebbles by the pebble surface combustion of a combustible gaseous mixture. Figure 2 is a plan View taken on line 2-2 of Figure 1. Figure 3 is a vertical cross-section through the wind-box and/or manifold of my apparatus showing a preferred means of regulating the amount of oxygen-containing gas which is mixed with fuel-gas. Figure 4 is a schematic view of a pebble heating apparatus showing the relation between the pebble heating and reactant chambers and the path of pebble recycle.`

In Figures 1 and 2, pebble heating chamber l0 comprises shell Il which enclos-es a wind-box or manifold 29, a pebble heating chamber I3 through which the pebbles flow and a nue-gas chamber 28. Shell Il is preferably a metal shell closed at its ends. Pebble heating chamber I3 is formed by a closed refractory wall I 2. The chamber maybe any shape but is preferably rectangular in horizontal and vertical cross-section, more preferably elongated rectangular, vertical and horizontal cross-sections as shown in Figures 1 and 2. While the height to diameter ratio of heating chamber I3 may be varied over a Wide range for different operations, I find that chambers having height to diameter ratios of from 11/221 to 4:1 are preferred. Wall i2 surrounding pebble heating chamber I3 may be formed from super-refractory and/or common refractory materials. Common refractory materials may include re brick or re clay re brick. Super-refractory materials may include silicon carbide, mullite, alumina or other suitable, re-` fractory materials having physical and chemical properties which give it sufficient strength to withstand a reasonably heavy load and a high temperature without substantial breakage or deterioration. Silicon carbide may be satisfactorily used in operations utilizing temperatures up to about 3000 E'. Mullite may also be satisfactorily used at temperatures up to about 30'00 F., while alumina may be satisfactorily used at temperatures up to about 3300o F. The above materials may be used at those temperatures without substantial oxidation or reaction with most conventionally used pebbles. The construction of one of the walls, preferably one of the end walls, of wall I2 is such that bricks used in its construction form a grillwork, which grillwork, in turn, forms a plurality of conduits or passageways I4 which communicate between the wind-box or manifold 29 and the pebble bed in pebble heating chamber I3. The other end wall or the wall opposite the wall containing conduits I4 is constructed so that the bricks used in its construction form a grillwork which grillwork, in turn, forms a plurality of conduits or passageways Il which communicate between pebble heating chamber It and the nue-gas chamber 28. The Side walls of wall I2 containing no passageways serve to insulate shell II. Wind-box 29 is disposed vertically on the outside of and in communication with wall I2 so that wall I2 in effect forms one side of the wind-box. One skilled in the art will appreciate that wind-box or manifold 29 may be disposed on the outside of wall I2 without using wall I2 to form one of its sides. Metal shell II which surrounds wind-box 29 is lined by insulating means I 8 which may be formed of super-refractory or common refractory materials. Insulating lining on the inside of windbox 29 may not be needed to protect shell II,

depending on the temperature level of the gases in wind-box 29. Fuel-gas conduits I extending through wind-box 29 supply fuel-gas to mix with air or an oxygen-containing gas passed into windbox 29 as hereinafter set forth. I prefer to extend fuel supply conduits I5 down into the passageways or conduits I 4, the passageways serving as mixers to mix a combustible mixture which is preferably directed inwardly and downwardly by the passageways into the pebble bed contained in pebble heating chamber I3. Conduits I4 may be of any suitable shape but are preferably conical in shape and so formed that the combustible materials or other gases used are directed downwardly and inwardly into the pebble bed by the conduits. Fuel-gas is supplied to conduits I5 by line 28 or other suitable means. Valves I9 in fuel-gas conduits I5 are used to regulate the amount of fuel-gas passed to passageways I4. In operation the products of surface combustion are withdrawn from pebble heating chamber I3 through passageways I'I and passed into nuegas chamber 28 which is disposed opposite windbox 29 and on the outside of wall I2. Wall I2 may or may not be used to form one side of chamber 28, as desired. Passageways Il formed in wall I2 opposite the wall containing combustible mixture conduits I4 may be -any suitable shape but are preferably inclined openings, slotshaped in vertical cross-section. The passageways extend upwardly and outwardly from pebble heating chamber Passageways II are preferably formed in wall I2 by laying the refractory bricks in a grill work manner to form the openings.

I3 to flue-gas chamber 28;

Shell II sur-` rounding lue-gas chamber 28 is lined Vwith in-.

sulating means I8 which may be super-refractory or common refractory materials. A conduit means 2! preferably located in the upper portion of fluegas chamber 28 is used to supply air and/or oxygen-containing gas to blend with and temper the flue-gases withdrawn from flue-gas chamber 28. Damper 3l in conduit 2I is used to regulate the amount of air or oxygen-containing gas passed to flue-gas chamber 28. A conduit 22 with blower 23 therein communicates between flue-gas chamber 2li and wind-box or manifold 29. Conduit 22 is used to recycle flue-gases. If desired, a conduit means to pass air or oxygen-containing gas into conduit 22 may be used. However, tempering the flue-gases prior to their introduction into conduit 22 is preferable since under usual temperature conditions no insulating lining is needed in conduit 22. A stack 24 preferably located Ibetween blower 23 and wind-box or manifold 29 in conduit 22 is used to withdraw excess flue-gases from the system, Damper 25 in stock 24 is used to control the amount of nue-gas withdrawn. Inlet means 2l is provided to pass pebbles into pebble heating chamber I3 and outlet means 28 is provided to withdraw heated pebbles from pebble heating chamber I3. e l d j If the pebble heater apparatus of my invention is operated at a substantial super-atmospheric pressure, the pressure in pebble heating chamber I3 will be above atmospheric pressure and, likewise, the pressure in flue-gas chamber 28 will be above atmospheric pressure. `Under these conditions, it would be impossible to admit air or an oxygen-containing gas `under atmospheric pressure into either flue-gas chamber 28 or recycle conduit 22. Instead, i-t would be possible and desirable to vent the excess flue-gas from conduit 22 or nue-gas chamber 28 as desired, and it would be necessary to compress an oxygen-containing gas and admit same into conduit 22 on either the upstream or downstream side of blower 23 depending upon specific conditions.

Figure 3 shows a preferred means to regulate the amount of air or oxygen-containing gas which is admitted to conduits I4 to be mixed with fuel-gas supplied by conduit I5 communicating between fuel supply means 20 and passageways l I4. Any means which wil1 vary the size of the openings of passageways I4 on the end nearest wind-box or manifold 29 will work, but I prefer to use means 38 which is a cylindrically shaped damper which may be moved up and down conduit I5 so as to vary the size of air passageway 3 I. I prefer to have a dampering means such as means 38 and a fuel-gas regulating means such as valve I9 to regulate the amount of oxygencontaining gas and fuel-gas supplied to each passageway I4 so that the heat input to any portion of the pebble bed in pebble heating chamber I3 may be controlled. Of course, the size of conduits or passageways I4 may be varied to accomplish the same result, but since varied operating conditions may be desired, I prefer -to have regu-n lation means to vary the amount of fuel-gas and oxygen-containing gas.

Figure 4 is a schematic diagram showing how the apparatus shown in Figures 1, 2 and 3 is utilized in a complete pebble heater system. lin Figure 4, shell II enclosing Wind-box or manifold 28, pebble heating chamber I3, and flue-gas chamber 28 is provided with pebble inlet 21 and pebble outlet 26, andi is connected to shell 32, enclosing a fluid heating chamber', by pebble outlet 26. 4Shell 32'is"provded in-its:upperportion associe with effluent outlet means such as conduit 36. Feed inlet means such as conduit 33 is provided in the lower portion of shell 32. Pebble outlet 34 is also provided in the lower portion of shell 32, and pebble transportation means, such as elevator 35, communicates between pebble outlet 34 in shell 32 and pebble inlet conduit 21 in the top of shell I I.

In the operation of the apparatus shown in Figures 1, 2, 3 and 4 of the drawings, pebbles made from any selected refractory material, suitable for 'the process to be carried on Within the apparatus are inserted into the upper portion of the heating chamber through pebble inlet 21. A fuel-gas and air mixture or a fuel-gas and an oxygen-containing gas mixture is provided by supplying fuel-gas through condui-ts I and vair or oxygen-containing gas from wind-box 29 to passageways I4. The gases are mixed into a combustible mixture in passageways Id and are passed inwardly and rdownwardly into the pebble bed in pebble heating chamber I3. Therein the hot pebbles heat the combustible mixture to its kindling temperature and the combustible mixture burns on the surface of the pebbles. The combustible mixture present in passageways I4 is at a temperature below its kindling temperature and is movingat a velocity greater than the velocity of flame propagation so that the mixture does not burn until it contacts the pebbles in the bed. The products of combustion are withdrawn through passageways I1 opposite passageways I4 and are passed into flue-gas chamber 28. The flow of gases being normal to the flow of pebbles. Air or an oxygen-containing gas is passed into flue-gas chamber 28 through conduit 2I and the air or oxygen-containing gas is mixed with the flue-gases prior to withdrawal of the resulting mixture from the ilue-gas chamber. When the pebble heating system is under normal operation a quantity of air or other oxygen-containing gas is added through conduit 2| in an amount suincient to provide the oxygen necessary to burn the fuel-gas passed through conduits I5 to passageways I4. If desired, a greater quantity of air or oxygen-containing gas may be added as a means of controlling the temperature within heating chamber I3. A resulting mixture of lluegases and air or oxygen-containing gas is withdrawn from flue-gas chamber 23 through conduit 22 containing blower 23 and is passed to windbox or manifold 29, in effect, recycling the products of combustion or nue-gases. A portion of the flue-gases tempered and blended with air is withdrawn from the system through stack 24 locatedin conduit 22 between blower 23 and windbox 29. Under normal operating conditions the same amount of flue-gases is withdrawn through stack 2li as the amount of air or oxygen-containing gas passed to lue-gas chamber through conduit 2 i. I prefer to add the air and oxygen-containing gas to blend with and temper the fluegases in the upper portion of nue-gas chamber 28 because addition at this point eliminates the necessity of insulating the inside of conduit 22. Flue-gases are preferably withdrawn from the system through a stack located in conduit 22 after blower 23 since this eliminates providing another blower to withdraw the flue-gases from the system. The heated pebbles pass downwardly through heating chamber I3 and reach a desired iinal temperature in the lower portion of pebble Aheating chamber I3 just prior to their withdrawal through pebble outlet meansZS. The heated pebbles vpass downwardly through pebble shell 32 as pebbles are withdrawn through pebble outlet 3d in the bottom of shell 32, the pebble bed being contiguous through the pebble heating and huid heating chambers. Under normal operations the pebble outlet and at least a portion of the fluid heating chamber and pebble heating chamber are lled with a moving bed of pebbles. In Some cases a pebble surge chamber may be arranged ahead of the pebble heating chamber in the pebble flow. When such an arrangement exists, sufficient pebbles may be supplied to entirely iill the space within the heating chamber Also, sometimes the fluid heating chamber is op erated so as to be completely iilled with pebbles. Material to be treated is injected into the lower portion of the iiuid heating chamber through inlet conduit 33. A fluid material rises through the iiuid heating chamber gaining heat from the downwardly flowing pebbles and passes out of the fluid heating chamber through eiiluent outlet conduit 36. Pebbles which have been cooled during the iiuid heating step pass out of the bottom of the fluid heating chamber and are carried by elevator 35 to the upper portion of the heating chamber within shell EI. Herein they are once again subjected to the pebble heating step described above.

In some instances, products of combustion may be carried from the pebble heating chamber into the fluid heating chamber with the pebbles, and heated products may rise from the uid heating chamber, through the pebble outlet conduit, into the pebble heating chamber. Such an occurrence would cause the conditions in either chamber to be unstable. For that reason, it may be desirable to provide conduit means for injecting into the pebble conduit between the chambers as a sealing means, a hot gas which is inert to the reaction. The sealing means would prevent other gases from passing therethrough.

The method and apparatus of my invention is particularly useful in pebble heater apparatus where carbon is deposited on the pebbles during the reaction step in the fluid heating chamber or where a catalytic pebble is being used such as in a catalytic hydrocarbon conversion process, and carbon is deposited on the catalyst reducing its eiiiciency. Under these conditions, I prefer to regenerate and heat the pebbles by admitting flue-gas containing oxygen, but without any combustible constituents, into the upper passageways I4 so as to burn the carbon from the catalyst or from the surface of the pebbles in the upper portion of the heating chamber in a relatively well-defined carbon burning zone in which the maximum temperature can be controlled by controlling the amount of oxygen-containing fluegas admitted. In operating this way no fuel-gas is supplied to passageways It in the upper or carbon burning zone of pebble heating chamber I3. In operating in this manner the additional heat necessary to raise the regenerated pebbles, catalytic or otherwise, to reaction temperature is supplied by the injection of a combustible gaseous mixture into the lower portion of the pebble bed through passageways i4 in the lower portion of heating chamber I3. By this procedure it is possible to prevent overheating of a catalyst during the burning 01T of the carbon. that is, by regulating the amount of oxygencontaining nue-gas admitted by adjusting regulating means 3d, and it is also possible to :actively control the temperature level to which the pebbles are inally raised prior to their entry into the reaction chamber, that is, by regulating the amount of fuel-gas and recycled flue-gases containing oxygen passed into the pebble bed in the lower portion of pebble heating chamber I3.

The process and apparatus of my invention can be operated successfully under various conditions in addition to the above mentioned example where carbon is deposited on the pebble in the fluid heating chamber. The following examples, as well as those previously set forth, are only typical and are not to be construed to unduly limit the scope of my invention.

In the case where a gaseous mixture of propane and ethane is being cracked in the uid heating chamber at a temperature of from 1300 to 1500 F., I find that usually the temperature of the pebbles recycled to the top of the pebble heating chamber is from 600 to 1000 F. Pebbles at a temperature within this range will not heat a combustible gaseous mixture to its kindling temperature; therefore, surface combustion cannot be carried out in the upper portion of the pebble heating chamber. In this case the fuel-gas 'is burned, that is, passageways i4 function as burners, and the products of combustion pass 'through pebble bed normal to its path of flow heating the pebbles to a temperature high enough so 'that surface combustion may be carried out at points lower in the heating chamber. In operating in this manner, I prefer to use the burner method of combustion in the upper 1A; to 1/3 of the pebble heating chamber.

A typical application of pebble heater apparatus is in the cracking of ethane at temperatures up to 2500 F., usually in the range of 1700 to 1900 F. Also, steam super-heating, air preheating or certain chemical reactions are sometimes carried out at these relatively high temperatures. In the aforementioned operations the pebbles are usually returned to the top of the pebble heating chamber at a temperature of from 1000 to 1500" F. When the pebbles are returned at this relatively high temperature they are hot enough so that pebble surface combustion may be carried out throughout the pebble t Another typical operation advantageously perl 'formed with pebble heater apparatus is that where a liquid or a liquid and gas mixture, such as a hydrocarbon mixture is converted in the huid heating chamber of pebble heater apparatus. tively high and the effluent product gases from the fluid heating chamber may be very hot having a temperature inthe range of 1700 to 2500" F., yet the pebbles contacting the entering relatively cold feed lose a large amount of their heat content. I find that in this case the pebbles returned to the top of the pebble heating chamber usually have a temperature of from 600 to 1000u F. In this case since the pebbles will not raise the combustible heating gas mixture to its kindling temperature in the upper portion of the pebble heating chamber, I find that it is necessary to operate with burners in the upper 1A; to 1/3 of the pebble heating chamber and with surface combustion in the lower 2%; to 3A of the pebble heating chamber as -hereinbefore described.

As will be evident to those skilled in the art various modifications of this invention can be made or followed in the lightof the foregoing disclosure, discussion and examples without de- The conversion temperature may be relaparting from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

l. In a pebble heater apparatus utilizing a gravitating bed of heated pebbles, an improved pebble heating chamber which comprises: a vertically disposed walled heating chamber; pebble inlet means in the upper portion of said heating chamber; pebble outlet means in the lower portion of said heating chamber; a windbox disposed on the outside of and in communication with the wall of said heating chamber; a plurality of passageways in the upper and lower portions of said heating chamber through said wall of said heating chamber communicating between points within said wind-box and points within said heating chamber; a flue-gas chamber on the outside of and in communication with the wall of said heating chamber, said flue-gas chamber being disposed opposite said wind-box; a plurality of flue-gas passageways through said wall of said heating chamber communicating between points within said heating chamber and points Within saidflue-gas chamber, said passageways being disposed opposite said firstnamed pasageways; a conduit communicating between the upper portion of said flue-gas chamber and the upper portion of said wind-box for recycling flue-gas tempered and blended with an oxygen-containing gas; a conduit in the upper portion of said flue-gas chamber communicating between a point outside said flue-gas chamber and a point insidesaid flue-gas chamber; a stack for withdrawing flue-gas disposed in said conduit communicating between said flue-gas chamber and said wind-box; and a fuel supplying means in said rst-named passageways.

2. In a pebble heater apparatus utilizing a gravitating bed of heated pebbles, an improved pebble heating chamber which comprises; an elongated vertically disposed refractory walled heating chamber; pebble inlet means in the upper portion of said heating chamber; pebble outlet means in the lower portion of said heating chamber; a wind-box disposed on the outside of and in communication with the wall of said heating chamber, said wind-box being disposed vertically along said heating chamber; a plurality of passageways in the upper and lower portions of said heating chamber through said wall of said heating chamber communicating between points within said wind-box and points within said heating chamber, said passageways being disposed at a plurality of elevations; a metal shelled refractory lined flue-gas chamber on the outside of and in communication with the wall of said heating chamber, said flue-gas chamber being disposed vertically along said heating chamber opposite said wind-box; a plurality of flue-gas passageways through said wall of said heating chamber communicating between points within said heating chamber and points within said fine-gas chamber, said passageways being disposed at a plurality of elevations and opposite said first-named passageways; a conduit having a blower therein communicating between the upper portion of said flue-gas chamber and the upper portion of said wind-box for recycling fluegas tempered and blended with air; a conduit in the upper portion of said flue-gas chamber communicating between a point outside said nue-gas chamber and a point inside said fine-gas chamber; a stack for withdrawing liuc-gas disposed between said blower and said wind-box in said conduit communicating between said flue-gas chamber and said wind-box; and conduits communicating between a fuel-gas supply means and said first-named passageways.

3. In a pebble heater apparatus utilizing a gravitating bed of heated pebbles, an improved pebble heating chamber which comprises: an elongated vertically disposed refractory walled heating chamber, having rectangular vertical and horizontal cross-sections; pebble inlet means in the upper portion of said heating chamber; pebble outlet means in the lower portion of said heating chamber; a wind-box disposed on the outside of and in communication with a wall of said heating chamber, said wind-box being disposed vertically along said wall of said heating chamber; a plurality of passageways in the upper and lower portions of said heating chamber through said wall of said heating chamber adjacent said wind-box communicating between points within said wind-box and points within said heating chamber, said passageways being disposed at a plurality of elevations, a metal shelled refractory lined flue-gas chamber on the outside of and in communication with a wall of said heating chamber, said flue-gas chamber being disposed vertically along said heating chamber opposite said wind-box; a plurality of flue-gas passageways through said wall of said heating chamber adiacent said fiue-gas chamber communicating between points within said heating chamber and points within said nue-gas chamber, said passageways being disposed at a plurality of elevations and opposite said rstnamed passageways: a conduit having a blower therein communicating between the upper portion of said flue-gas chamber and the upper portion of said wind-box for recycling flue-gas tempered and blended with air; a conduit in the upper portion of said flue-gas chamber communicating between a point outside said flue-gas chamber and a point inside said nue-gas chamber; a sta-ck for withdrawing flue-gas disposed between said blower and said wind-box in said conduit communicating between said flue-gas chamber and said wind-box; and conduits communicating between a fuel-gas supply means and each of said first-named passageways.

4. In a pebble heater apparatus utilizing a gravitating bed of heated pebbles, an improved pebble heating chamber which comprises: an elognated vertically disposed refractory walled heating chamber, having rectangular vertical and horizontal cross-sections: pebble inlet means in the upper portion of said heating chamber; pebble outlet means in the lower portion of said heating chamber; a wind-box disposed on the outside of and in communication with a wall of said heating chamber, said wind-box being disposed vertically along said wall of said heating chamber; a plurality of passageways in the upper and lower portions of said heating chamber through the wall of said heating chamber adiacent said wind-box communicating between points within said wind-box and points within said heating chamber, said passageways being disposed at a plurality of elevations and directed inwardly and downwardly; a metal shelled refractory lined flue-gas chamber on the outside of and in communication with a wall of said heating chamber, said nue-gas chamber being disposed vertically along said heating chamber on the wall opposite said wind-box; a plurality of flue-gas passageways through the wall of said heating chamber adjacent said flue-gas chamber communicating between points Within said heat- 12 ing chamber and points within said flue-gas chamber, said passageways being disposed at` a plurality of elevations and opposite said irstnamed passageways and directed upwardly and outwardly; a conduit having a blower therein communicating between the upper portion of said flue-gas chamber and. the upper portion of said wind-box for recycling flue-gas tempered and blended with air; a conduit in the upper portion of said flue-gas chamber communicating betweenv a point outside said ilus-gas chamber and a point inside said nue-gas chamber; a stack for withdrawing flue-gas disposed between said blower and said wind-box in said conduit communicating between said flue-gas chamber and said windbox; and conduits communicating between a fuel-gas supply means and each of said first-named passageways.

5. In a pebble heater apparatus utilizing a gravitating bed of heated pebbles, an improved pebble heating chamber which comprises: an elongated vertically disposed heating chamber, having rectangular vertical and horizontal crosssections; pebble inlet means in the upper portion of said heating chamber; pebble outlet means in the lower portion of said heating chamber; a shell cooperating with a wall of said heating chamber to form a manifold, said manifold being disposed vertically along said heating chamber; a plurality of passageways formed in the upper and lower portions of said wall inter-connecting said manifold and said heating chamber, said passageways being disposed at a plurality of elevations and directed inwardly and downwardly; a shell cooperating with the wall. of said heating chamber opposite said manifold to form a fluegas chamber, said flue-gas chamber being disposed vertically along said heating chamber; a plurality of flue-gas passageways formed in said last-mentioned wall connecting said heating chamber and said flue-gas chamber, said passageways being disposed at a plurality of elevations and opposite said first-named passageways and directed upwardly and outwardly; a conduit having a blower therein communicating between the upper portion of said fine-gas chamber and the upper portion of said manifold for recycling flue-gas tempered andl blended with an oxygen-containing gas; an inlet conduit in the upper portion of said flue-gas chamber; a stack for withdrawing flue-gas disposed between said blower and said manifold in said conduit that communicates between said flue-gas chamber and said manifold; and a fuel supplying means in said first-named passageways.

6. In a pebble heater apparatus utilizing a gravitating bed of heated, 1/8 inch to 1 inch, spherical pebbles, an improved pebble heating chamber which comprises: a vertically disposed refractory Walled heating chamber, having elongated rectangular vertical and horizontal crosssections; pebble inlet means in the upper portion of said heating chamber; pebble outlet means in the lower portion of said heating chamber; a metal shelled refractory lined Wind-box disposed on the outside of and in communication with one of the end walls of said rectangularly shaped heating chamber, said wind-box being disposed vertically along said end-wall; a plurality of passageways in the upper and lower portions of said heating chamber through said end wall communicating between points within said wind-boxand points within said heating chamber, said passageways being disposed in rows at a plurality of elevations and directed inwardly and downwardly; a metal shelled refractory lined liuc-gas chamber on the outside of and in communication with the opposite end wall of said rectangularly shaped heating chamber, said flue-gas chamber being disposed vertically along said opposite end wall; a plurality of nue-gas passageways through said opposite end wall communicating between points within said heating chamber and points within said uegas chamber, said passageways being disposed in rows at a plurality of elevations and directed outwardly and upwardly; an air-inlet conduit communicating with said flue-gas chamber; a conduit having a blower therein communicating between the upper portion of said flue-gas chamber and the upper portion of said wind-box for continuously recycling flue-gas tempered and blended with air; a stack in said last-named conduit disposed between said blower and said windbox for withdrawing flue-gas; and conduits communicating between a fuel-gas supply means and each of said passageways in said first-named end wall, said conduits extending into said passageways.

7. In a pebble heater system utilizing a gravitating bed of heated pebbles, the method of heating said pebbles which comprises: introducing refractory pebbles into a pebble heating zone; mixing fuel-gas and an oxygen-containing gas in a plurality of mixing zones; introducing resulting combustible mixtures of fuel-gas and an oxygen-containing gas into said pebble bed at a plurality of points, said resulting mixtures being introduced normal to the path of flow of said pebbles at a velocity greater than the velocity of flame propagation of the said mixtures: burning said resulting mixtures within the interstices of the surface of said pebbles; withdrawing flue-gas from said pebble heating zone at a plurality of points; mixing an oxygen-containing gas with said withdrawn nue-gas; withdrawing a portion of a resulting mixture from said system and recyling a further portion of said resulting mixture to said first-named mixing step: and withdrawing heated pebbles from the bottom portion of said pebble heating zone.

8. In a pebble heater heater system utilizing a gravitating bed of heated pebbles, the method of heating said pebbles which comprises: introducing spherical refractory pebbles having a diameter of from 1/8 inch to 1 inch into the upper portion of a pebble heating zone; introducing fuel-gas into a plurality of mixing zones; introducing flue-gas tempered and blended with air into said mixing zones; mixing said fuel-gas and said ue-gas in said mixing zones; introducing resulting combustible mixtures into said pebble heating zone normal to the path of iiow of said pebbles and at a plurality of points in the upper and lower portions of said heating zone at a velocity greater than the velocity of name propagation of the said mixtures, said combustion mixture directly contacting said pebbles: burning said resulting combustible mixture within the interstices of the surface of said pebbles; withdrawing products of combustion from said heating zone at a plurality of points in l@he upper and lower portions of said heating zone and passing same to a flue-gas withdrawal zone; introducing air into said withdrawal zone in quantity sufficient to furnish oxygen to burn said fuel-gas introduced into said mixing zones and mixing same with said products of combustion; withdrawing a portion of a resulting mixture of flue-gas and air from said system; recycling a portion of said '14 resulting mixture oi. flue-gas and air to said firstnamed mixing zones as said nue-gas tempered and blended with air introduced into said iirstnamed mixing zones, and withdrawing heated pebbles from the bottom portion of said heating zone.

9. In a pebble heater system utilizing a gravitating bed of heated pebbles, the method of heating said pebbles which comprises; introducing spherical refractory pebbles having a diameter from 1/8 to 1 inch into a pebble heating zone; introducing fuel-gas into a plurality of mixing zones; introducing ue-gas tempered and blended with air into said mixing zones; mixing said fuel-gas and said nue-gas in said mixing zones; introducing resulting combustible mixtures into said pebble heating zone normal to the path of iow of said pebbles and at a plurality of points in the upper and lower portions of said heating zone at a velocity greater than the velocity of flame propagation of the said mixtures, said combustible mixtures directly contacting said pebbles; burning said resulting combustible mixtures within the interstices of the surface of said pebbles; withdrawing products of combustion from said heating zone at a plurality of points in the upper and lower portions of said heating zone and passing same to a flue-gas withdrawal zone; introducing air into said withdrawal zone in quantity suiicient to furnish oxygen to burn said fuel-gas introduced into said mixing zones and mixing same with said products of combustion; withdrawing a portion of a resulting mixture of nue-gas and air from said system; recycling a portion of said resulting mixture of nue-gas and air to said first-named mixing zones as said flue-gas tempered and blended with air introduced into said first-named mixing zones; withdrawing heated pebbles from the bottom portion of said heating zone and passing same into the upper portion of a fluid heating zone; introducing a uid stream into the lower portion of said fluid heating zone and passing same in direct contact with and countercurrent to the flow of said pebbles in said fluid heating zone; withdrawing a fluid stream from the upper portion of said fluid heating zone; withdrawing cooled pebbles from the bottom portion of said fluid heating zone; and recycling said cooled pebbles to the upper portion of said pebble heating zone.

10. In a pebble heater apparatus utilizing a gravitating bed of heated pebbles, an improved pebble heating chamber which comprises: a vertically disposed walled heating chamber; pebble inlet means in the upper portion of said heating chamber: pebble outlet means in the lower portion of said heating chamber; a wind-box disposed on the outside of and in communication with the wall of said heating chamber; a plurality of passageways in the upper and lower portions of said heating chamber through said wall of said heating chamber communicating be tween points within said wind-box and said heating chamber; a nue-gas chamber on the outside of and in communication with the wall of said heating chamber, said flue-gas chamber being disposed opposite said wind-box; a plurality of flue-gas passageways through said wall of said heating chamber communicating between points within said heating chamber and points within said flue-gas chamber, said passageways being disposed opposite said first-named passageways; means for recycling flue-gas from said ue-gas chamber to said wind-box; means for adding an oxygencontainingy gas to said recycle flue-gas; means, for withdrawing excess nue-gas; fuel supplying means in said first-named passageways.

11. An improved method of regenerating and heating pebbles which are contaminated with surface deposits of carbon, which comprises; introducing said pebbles into a pebble heating Zone; laterally introducing an oxygen-containing nuegas into the upper portion of said heating zone at a plurality of points and contacting said pebbles with said nue-gas whereby carbon is burned from said pebbles in said upper portion of said heating zone; introducing fuel-gas into a plurality of mixing Zones; introducing an oxygencontaining nue-gas into said mixing zones; mixing said fuel-gas and said last-mentioned fluegas in said mixing zones; laterally introducing resulting combustible mixtures into the lower portion of said heating Zone at a plurality ci points at a velocity greater than the velocity of i'iame propagation of the said mixtures whereby the mixture does not burn until it contacts said pebbles in said heating Zone, said combustible mixtures directly contacting said pebbles; burning said resulting combustible mixtures within the interstices of the surface of said pebbles; withdrawing products of combustion from said heating zone at a plurality of points in the upper and lower portions of said heating zone; introducing an oxygen-containing gas into said withdrawn products of combustion; withdrawing a portion of the resulting mixture or flue-gas and an oxygen-containing gas from the system; recycling a portion of said resulting mixture to said mixing zones; and withdrawing heated pebbles from the bottom portion of said heating zone.

l2. In the operation of a pebble heater system utilizing a gravitating bed of heated pebbles, wherein pebbles to be heated have carbonaceous material deposited thereon, the method of heating said pebbles which comprises: introducing spherical refractory pebbles having a diameter of from 1/8 inch to 1 inch into the upper portion of a pebble heating zone; introducing fuel-gas into a plurality of mixing zones; introducing flue-gas tempered and blended with an oxygen-containing gas into said mixing Zones, mixing said fuelgas and said flue-gas in said mixing zones and introducing resulting combustible mixtures into said pebble heating zone normal to the path of flow of said pebbles and at a plurality of points in the lower portion of said heating zone, said combustion mixtures directly contacting pebbles therein; burning said resulting combustible mixtures on the surface of said pebbles in the lower portion of said pebble heating zone; introducing flue-gas tempered and blended with an oxygencontaining gas into said pebble heating zone normal to the path of now of said pebbles and at a plurality of points in the upper portion of said heating zone, said flue-gas tempered and blended with oxygen-containing gas directly contacting pebbles therein thereby burning carbonaceous material on said pebbles in the upper portion of said pebble heating zone; withdrawing products of combustion from said pebble heating Zone at a plurality of points in the upper and lower portions of said heating zone and passing saine into a flue-gas withdrawal zone; adding an oxygencontaining gas to said combustion products; withdrawing a portion of a resulting mixture from the system, passing a second portion of said mixture into said mixing zones and passing a portion of said mixture in said mixing zone into the upper portion of said pebble heating Zone, as said flue-gas tempered and blended with an oxygen-containing gas.

18. The apparatus of claim 6 wherein each of said conduits communicating between a fuelgas supply means and each of said passageways in said first-named end wall is equipped with an adjustable damper adapted to vary the size of passageways delineated by (1) said damper; (2) said passageways, in said first-named end wall; and 8) said conduits extending into said passageways in said first-named end wall.

LOUS J. WEBER.

REFERENCES CTED The following references are of record in the nie of this patent:

UNITED STATES PATENTS Number Name Date 508,542 Greer Nov. 14, 1893 692,257 Eldred Feb. 4, 1902 1,554,866 Leslie Dec. 8, 1925 2,398,954 Odell Apr. 23, 1946 2,412,025 Zimmerman Dec.,3, 1946 2,445,351 Gohr July 20, 1948 2,445,554 Bergstrom July 20, 1948 2,457,837 Simpson et al. Jan. 4, 1949 2,458,359 Evans Jan. 4, 1949 2,541,548 Robinson Feb. 13, 1951 2,551,905 Robinson May 8, 1951 FOREIGN PATENTS Number Country Date 115,232 Great Britain Apr. 10, 1919 

11. AN IMPROVED METHOD OF REGENERATING AND HEATING PEBBLES WHICH ARE CONTAMINATED WITH SURFACE DEPOSITS OF CARBON, WHICH COMPRISES; INTRODUCING SAID PEBBLES INTO A PEBBLE HEATING ZONE; LATERALLY INTRODUCING AN OXYGEN-CONTAINING FLUEGAS INTO THE UPPER PORTION OF SAID HEATING ZONE AT A PLURALITY OF POINTS AND CONTACTING SAID PEBBLES WITH SAID FLUE-GAS WHEREBY CARBON IS BURNED FROM SAID PEBBLES IN SAID UPPER PORTION OF SAID HEATING ZONE; INTRODUCING FUEL-GAS INTO A PLURALITY OF MIXING ZONES; INTRODUCING AN OXYGENCONTAINING FLUE-GAS INTO SAID MIXING ZONES; MIXING SAID FUEL-GAS AND SAID LAST-MENTIONED FLUEGAS IN SAID MIXING ZONES; LATERALLY INTRODUCING RESULTING COMBUSTIBLE MIXTURES INTO THE LOWER PORTION OF SAID HEATING ZONE AT A PLURALITY OF POINTS AT A VELOCITY GREATER THAN THE VELOCITY OF FLAME PROPAGATION OF THE SAID MIXTURES WHEREBY THE MIXTURE DOES NOT BURN UNTIL IT CONTACTS SAID PEBBLES IN SAID HEATING ZONE, SAID COMBUSTIBLE MIXTURES DIRECTLY CONTACTING SAID PEBBLES; BURNING SAID RESULTING COMBUSTIBLE MIXTURES WITHIN THE INTERSTICES OF THE SURFACE OF SAID PEBBLES; WITHDRAWING PRODUCTS OF COMBUSTION FROM SAID HEATING ZONE AT A PLURALITY OF POINTS IN THE UPPER AND LOWER PORTIONS OF SAID HEATING ZONE; INTRODUCING AN OXYGEN-CONTAINING GAS INTO SAID WITHDRAWN PRODUCTS OF COMBUSTION; WITHDRAWING A PROTION OF THE RESULTING MIXTURE OF FLUE-GAS AND AN OXYGEN-CONTAINING GAS FROM THE SYSTEM; RECYCLING A PORTION OF SAID RESULTING MIXTURE TO SAID MIXING ZONES; AND WITHDRAWING HEATED PEBBLES FROM THE BOTTOM PORTION OF SAID HEATING ZONE. 